3 - Using the Telecoms-Trainer 101 to model equations

Transcription

1 Name: Class: 3 - Using the Telecoms-Trainer 101 to model equations

2 Experiment 3 Using the Telecoms-Trainer 101 to model equations Preliminary discussion This may surprise you, but mathematics is an important part of electronics and this is especially true for communications and telecommunications. As you ll learn, the output of all communications systems can be described mathematically with an equation. Although the math that you ll need for this manual is relatively light, there is some. Helpfully, the Emona Telecoms-Trainer 101 can model communications equations to bring them to life. The experiment This experiment will introduce you to modelling equations by using the Emona Telecoms-Trainer 101 to implement two relatively simple equations. It should take you about 45 minutes to complete this experiment. Equipment Emona Telecoms-Trainer 101 (plus power-pack) Dual channel 20MHz oscilloscope two Emona Telecoms-Trainer 101 oscilloscope leads assorted Emona Telecoms-Trainer 101 patch leads Emona Instruments Experiment 3 Using the Telecoms-Trainer 101 to model equations

3 Something you need to know for the experiment This box contains the definition for an electrical term used in this experiment. Although you ve probably seen it before, it s worth taking a minute to read it to check your understanding. When two signals are 180 out of phase, they re out of step by half a cycle. This is shown in Figure 1 below. As you can see, the two signals are always travelling in opposite directions. That is, as one goes up, the other goes down (and vice versa). Figure 1 Experiment 3 Using the Telecoms-Trainer 101 to model equations 2008 Emona Instruments 3-3

4 In this part of the experiment, you re going to use the Adder module to add two electrical signals together. Mathematically, you ll be implementing the equation: Adder module output = Signal A + Signal B Procedure 1. Gather the equipment listed on page Set up the scope per the instructions in Experiment 1. Ensure that: the Trigger Source control is set to the CH1 (or INT) position. the Mode control is set to the CH1 position. 3. Locate the Adder module and set its G and g controls to about the middle of their travel. 4. Connect the set-up shown in Figure 2 below. Note: Although not shown, insert the black plugs of the oscilloscope leads into a ground (GND) socket. Figure 2 This set-up can be represented by the block diagram in Figure 3 on the next page Emona Instruments Experiment 3 Using the Telecoms-Trainer 101 to model equations

5 Figure 3 5. Adjust the scope s Timebase control to view two or so cycles of the Master Signals module s 2kHz SINE output. 6. Disconnect the lead to the Adder module s B input. 7. Measure the amplitude (peak-to-peak) of the Master Signals module s 2kHz SINE output. Record your measurement here: 8. Set the scope s Mode control to the CH2 position. 9. Adjust the Adder module s G control until its output voltage is the same size as its input voltage (measured in Step 7). Note: This makes the gain for the Adder module s A input Reconnect the lead to the Adder module s B input. 11. Disconnect the lead to the Adder module s A input. 12. Adjust the Adder module s g control until its output voltage is the same size as its input voltage (measured in Step 7). Note: This makes the gain for the Adder module s B input -1 and means that the Adder module s two inputs should have the same gain. 13. Reconnect the lead to the Adder module s A input. Experiment 3 Using the Telecoms-Trainer 101 to model equations 2008 Emona Instruments 3-5

6 The set-up shown in Figures 3 and 4 is now ready to implement the equation: Adder module output = Signal A + Signal B Notice though that the Adder module s two inputs are the same signal a 4Vp-p 2kHz sinewave. So, with values the equation is: Adder module output = 4Vp-p (2kHz sine) + 4Vp-p (2kHz sine) When the equation is solved, we get: Adder module output = 8Vp-p (2kHz sine) Let s see if this is what we get in practice. 14. Set the scope s Mode control to the CH1 position. 15. Measure the amplitude of the Master Signals module s 2kHz SINE output. Record your measurement in Table 1 below. Note: The voltage may be a little different to that measured in Step 7 due to loading of the Master Signals module s 2kHz SINE output. 16. Set the scope s Mode control to the CH2 position. 17. Measure and record the amplitude of the Adder module s output. Table 1 Input voltage Output voltage Emona Instruments Experiment 3 Using the Telecoms-Trainer 101 to model equations

7 Question 1 Is the Adder module s measured output voltage exactly 8Vp-p as theoretically predicted? Question 2 What are two reasons for this? Ask the instructor to check your work before continuing. Experiment 3 Using the Telecoms-Trainer 101 to model equations 2008 Emona Instruments 3-7

8 In the next part of the experiment, you re going to add two electrical signals together but one of them will be phase shifted. Mathematically, you ll be implementing the equation: Adder module output = Signal A + Signal B (with phase shift) 18. Locate the Phase Shifter module and set its Phase Change control to the 180 position. 19. Set the Phase Shifter module s Phase Adjust control about the middle of its travel. 20. Connect the set-up shown in Figure 4 below. Note: Insert the black plugs of the oscilloscope leads into a ground (GND) socket. Figure 4 This set-up can be represented by the block diagram in Figure 5 on the next page Emona Instruments Experiment 3 Using the Telecoms-Trainer 101 to model equations

9 Figure 5 The set-up shown in Figures 4 and 5 is now ready to implement the equation: Adder module output = Signal A + Signal B (with phase shift) The Adder module s two inputs are still the same signal a 4Vp-p 2kHz sinewave. So, with values the equation is: Adder module output = 4Vp-p (2kHz sine) + 4Vp-p (2kHz sine with phase shift) As the two signals have the same amplitude and frequency, if the phase shift is exactly 180 then their voltages at any point in the waveform is always exactly opposite. That is, when one sinewave is +1V, the other is -1V. When one is +3.75V, the other is -3.75V and so on. This means that, when the equation above is solved, we get: Adder module output = 0Vp-p Let s see if this is what we get in practice. Experiment 3 Using the Telecoms-Trainer 101 to model equations 2008 Emona Instruments 3-9

10 21. Set the scope s Mode control to the DUAL position to view the Phase Shifter module s output as well as the Master Signals module s 2kHz SINE output. 22. Adjust the Phase Shifter module s Phase Adjust control until the two signals look like they re 180 out of phase with each other. 23. Disconnect the scope s Channel 2 lead from the Phase Shifter module s output and connect it to the Adder module s output. 24. Set the scope s Mode control to the CH2 position. 25. Measure the amplitude of the Adder module s output. Record your measurement in Table 2 (on the next page). Tip: You ll probably need to adjust the Channel 2 Vertical Attenuation control to obtain an appropriate display (try the 0.1V/div setting). Table 2 Output voltage Question 3 What are two reasons for the output not being 0V as theoretically predicted? Ask the instructor to check your work before continuing Emona Instruments Experiment 3 Using the Telecoms-Trainer 101 to model equations

11 The following procedure can be used to adjust the Adder and Phase Shifter modules so that the set-up has a null output. That is, an output that is close to zero volts. 26. Vary the Phase Shifter module s Phase Adjust control left and right and observe the effect on the Adder module s output. 27. Adjust the Phase Shifter module s Phase Adjust control to obtain the smallest output voltage. Question 5 What can be said about the phase shift between the signals on the Adder module s two inputs now? 28. Vary the Adder module s g control left and right and observe the effect on the Adder module s output. 29. Adjust the Adder module s g control to obtain the smallest output voltage. Question 6 What can be said about the gain of the Adder module s two inputs now? Ask the instructor to check your work before finishing. Experiment 3 Using the Telecoms-Trainer 101 to model equations 2008 Emona Instruments 3-11

12 Emona Instruments Experiment 3 Using the Telecoms-Trainer 101 to model equations